I am guessing a lot of you have already heard this but i just encountered it today and thought it was pretty cool so i decided to share it.

There are three dragons, each with green eyes in a room. They can each see each other's eyes, but not their own. The following statement is said aloud and the dragon's regard it as true: "There is at least one dragon with green eyes". What new information do each of the dragon's gain from this statement?

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I used to view myself as a crow. A large, negative, angry bird who is portrayed as the sign of a bad omen. Feared by others and wanting to dominate, I was my own flock.

Also looked up solution, and I can confirm that a REQUIREMENT in the stating of this riddle is that the Green Dragons must leave the room when they discover they have green eyes. Without that, there is no logical reason that the Green Dragons learn any new information.

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Quote:

"If you refuse to use rock, you will never beat scissors." — Galef, Dakka Dakka Forums

I looked at this thread without having heard the solution, but knew that, from a meta-logical standpoint, each dragon must be able to derive its own eye color as green. There is no other hidden information to a dragon and it wouldn't be much of a riddle if the answer was "nothing happens". However, I couldn't arrive at the mechanism by which this would occur. I looked up the answer, and yeah, the automatic midnight birdification is kind of necessary to the puzzle because it creates the feedback loop of information that eventually leads the dragons to derive their own eye color

The bird clause isn't necessary and the solution to this puzzle is different from the solution to the puzzle from which this is derived from. The answer is:

[spoiler]Each dragon learns that from the possible perspective of another dragon, the third dragon can't possibly think that all three dragons have non-green eyes.[/spoiler]

response + answer to the other riddle

Yes, but each dragon already knew that, since they can see two other dragons with green eyes, therefore instantly excluding that all three have non-green eyes without anyone needing to say the "at least 1 dragon has green eyes". So I don't understand how there's any "new information" here.

_________________

Quote:

"If you refuse to use rock, you will never beat scissors." — Galef, Dakka Dakka Forums

The bird clause isn't necessary and the solution to this puzzle is different from the solution to the puzzle from which this is derived from. The answer is:

[spoiler]Each dragon learns that from the possible perspective of another dragon, the third dragon can't possibly think that all three dragons have non-green eyes.[/spoiler]

response + answer to the other riddle

Yes, but each dragon already knew that, since they can see two other dragons with green eyes, therefore instantly excluding that all three have non-green eyes without anyone needing to say the "at least 1 dragon has green eyes". So I don't understand how there's any "new information" here.

Spoiler

That "Information" is really convoluted, as its information on information, not information on facts. Essentially

Dragon 1 sees that dragons 2 and 3 have green eyes. Dragon 1's knowledge is ?GGDragon 1 knows that Dragon 2 sees ??G. But what does Dragon 1 Know that dragon 2 knows that dragon 3 knows? Well, any dragon knows that its own eye color is ? (aka it doesn't know) so Dragon 1 knows 2 must think 3 knows _ _ ?. Since Dragon 2 doesn't know its own eye color, dragon two only knows that dragon three sees _?? And since Dragon 1 is not privelaged to know its own eye color, dragon 1 cannot know what dragon 2 knows about dragon 3's opinions. So "Dragon 1 does not know that dragon 2 knows that dragon 3 knows there is at least one Green Eyed Dragon"

Once the voice speaks, all dragons know there is at least one green-eyed dragon, and they know that they all know, so Dragon 1 now knows that dragon 2 knows that dragon 3 knows there is a green eyed dragon.

The bird clause isn't necessary and the solution to this puzzle is different from the solution to the puzzle from which this is derived from. The answer is:

--

response + answer to the other riddle

Yes, but each dragon already knew that, since they can see two other dragons with green eyes, therefore instantly excluding that all three have non-green eyes without anyone needing to say the "at least 1 dragon has green eyes". So I don't understand how there's any "new information" here.

Spoiler

tevish explained it already, but its about what they learn about the other dragon's perspectives, not what they learn about the other dragon's eyes. Each dragon already knows that there are at least two other dragons with green eyes, but each dragon doesn't know that each other dragon knows that (as a simple example, from any dragon's perspective, if they have blue eyes, then from any other dragon's perspective, they only know that there is at least one dragon with green eyes)

_________________

I used to view myself as a crow. A large, negative, angry bird who is portrayed as the sign of a bad omen. Feared by others and wanting to dominate, I was my own flock.

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